1. Field
A compound for an organic optoelectronic device being capable of providing an organic optoelectronic device having excellent life-span, efficiency, electrochemical stability, and thermal stability, an organic light emitting diode including the compound, and a display device including the organic light emitting diode are disclosed.
2. Description of the Related Art
An organic optoelectronic device is, in a broad sense, a device for transforming photo-energy to electrical energy, or conversely, a device for transforming electrical energy to photo-energy.
An organic optoelectronic device may be classified in accordance with its driving principles. A first organic optoelectronic device is an electronic device driven as follows: excitons are generated in an organic material layer by photons from an external light source; the excitons are separated into electrons and holes; and the electrons and holes are transferred to different electrodes as a current source (voltage source).
A second organic optoelectronic device is an electronic device driven as follows: a voltage or a current is applied to at least two electrodes to inject holes and/or electrons into an organic semiconductor positioned at an interface of the electrodes, and the device is driven by the injected electrons and holes.
Examples of the organic optoelectronic device include an organic light emitting diode, an organic solar cell, an organic photoconductor drum, an organic transistor, and the like, which require a hole injecting or transport material, an electron injecting or transport material, or a light emitting material.
Particularly, an organic light emitting diode (OLED) has recently drawn attention due to an increasing demand for flat panel displays. In general, organic light emission refers to conversion of electrical energy into photo-energy.
An organic light emitting diode can convert electrical energy into light by applying current to an organic light emitting material. It has a structure in which a functional organic material layer is interposed between an anode and a cathode. The organic material layer includes a multi-layer including different materials, for example a hole injection layer (HIL), a hole transport layer (HTL), an emission layer, an electron transport layer (ETL), and an electron injection layer (EIL), in order to improve efficiency and stability of an organic light emitting diode.
In such an organic light emitting diode, when a voltage is applied between an anode and a cathode, holes from the anode and electrons from the cathode are injected to an organic material layer and recombined to generate excitons having high energy. The generated excitons generate light having certain wavelengths while shifting to a ground state.
Recently, it has become known that a phosphorescent light emitting material may be used as a light emitting material of an organic light emitting diode in addition to the fluorescent light emitting material. Such a phosphorescent material emits lights by first transporting the electrons from a ground state to an exited state, then transiting a singlet exciton to a triplet exciton through intersystem crossing, and finally transiting a triplet exciton to a ground state to emit light.
In an organic light emitting diode, an organic material layer includes a light emitting material and a charge transport material, for example a hole injection material, a hole transport material, an electron transport material, an electron injection material, and the like.
The light emitting material is classified as blue, green, and red light emitting materials according to emitted colors, and yellow and orange light emitting materials which emit colors approaching natural colors.
When a material is used as a light emitting material, its maximum light emitting wavelength can be shifted to a long wavelength or its color purity can decrease because of interactions between molecules. In addition, device efficiency can decrease because of a light emitting quenching effect. Therefore, a host/dopant system is included for a light emitting material in order to improve color purity and increase luminous efficiency and stability through energy transfer.
In order to achieve excellent performance of an organic light emitting diode, a material for an organic material layer, for example a hole injection material, a hole transport material, a light emitting material, an electron transport material, an electron injection material, and a light emitting material such as a host and/or a dopant, should be stable and have good efficiency. However, development of such a material has thus far been elusive and there is still a need for an improved material for an organic light emitting diode and other organic optoelectronic devices.
A low molecular organic light emitting diode is manufactured as a thin film in a vacuum deposition method, and can have good efficiency and life-span. A polymer organic light emitting diode manufactured in an Inkjet or spin coating method has an advantage of low initial cost and being large-sized.
Both low molecular organic light emitting and polymer organic light emitting diodes have an advantage of self-light emitting, high speed response, wide viewing angle, ultra-thinness, high image quality, durability, large driving temperature range, and the like. In particular, they have good visibility due to the self-light emitting characteristic. Compared with a liquid crystal display (“LCD”), an organic light emitting display (“OLED”) can be up to about one third thinner and lighter, because they do not need a backlight.
In addition, since they have a response speed of a microsecond unit, which is 1000 times faster than an LCD, they can realize a motion picture without an after-image. Based on these advantages, they have been remarkably developed to be 80 times more efficient and to have a 100 times longer life-span since they first came out in the late 1980's. Recently, they have become rapidly larger such that a 40-inch organic light emitting diode panel is now possible.
In order for the organic light emitting diode panel to be larger, it is necessary that the organic light emitting diodes have improved luminous efficiency and improved life-span at the same time. Luminous efficiency requires smooth combination between holes and electrons in an emission layer. However, since an organic material in general has slower electron mobility than hole mobility, it has a drawback of inefficient combination between holes and electrons. Accordingly, increasing electron injection and mobility from a cathode and simultaneously preventing movement of holes is required.
In order to improve the life-span, it is required to prevent material crystallization caused by Joule heat generated during device operation. Accordingly, there has been a strong need for an organic compound having excellent electron injection and mobility, and high electrochemical stability.